1. Field of the Invention
The invention relates to a process for preparing sulfonated phenyl carbonic acid esters having a quaternary group, which esters are useful as bleach precursors in detergent compositions.
2. The Prior Art
Detergent compositions that rely upon sodium perborate as a bleach normally require a precursor to activate the oxygen-releasing compound where wash-water temperatures are below 60.degree. C. A recently issued patent, U.S. Pat. No. 4,751,015 (Humphreys et al.), reported an exceptionally effective bleach precursor family of compounds identified as quaternary ammonium or phosphonium substituted peroxy carbonic acid esters. These precursors were reported synthesized in a two-step procedure. Illustrative is 2-(N,N,N-trimethylammonium)ethyl sodium 4-sulphophenyl carbonate chloride (SPCC) which was synthesized by first preparing choline chloroformate chloride through reaction of phosgene with choline chloride in a chloroform solution. The choline chloroformate chloride was then isolated as a crystalline solid. In a second step, the solid choline chloroformate chloride was added to an aqueous solution of sodium 4-phenol sulfonate containing an equimolar amount sodium hydroxide.
A number of problems are associated with this process. For instance, there are handling difficulties with choline chloroformate chloride, a highly hygroscopic material. Spontaneous crystallization of the chloroformate from solution has been noted. This presents a challenge in commercial production to avoid pipeline constriction. Furthermore, yields of the final product, SPCC, are variable, sometimes being even quite poor (40-85%). Instability of the final product is a still further problem.
Final bleach precursor product, e.g. SPCC, resulting from this process normally contains a very substantial amount of sodium chloride. This by-product is undesirable for several reasons. Sodium chloride promotes corrosion of certain metallic parts of washing machines. Further, sodium chloride takes up valuable space within a detergent formulation without contributing any useful function.
Another synthetic route has been suggested which involves a direct sulfonation reaction. More than one equivalent of sulfonating agent (e.g. sulfur trioxide) normally is required in the sulfonation of quaternary ammonium, phosphonium or sulfonium substituted aryl esters of carbonic or carboxylic acids when the associated counterion has basic or nucleophilic properties. This requirement results from the counterion complexing quite strongly with the sulfonating agent. For instance, chloride complexes with sulfur trioxide to form ClSO.sub.3.sup.-. Similarly, the bisulfate anion and sulfate dianion complexes with sulfur trioxide forming HS.sub.2 O.sub.7.sup.- and S.sub.2 O.sub.7.sup.=, respectively.
Problems of counterion complexing can be overcome if the ester is sulfonated with oleum, a procedure reported in co-pending U.S. patent application Ser. No. 07/272,143. Therein the actual sulfonating agent is the sulfuric acid component of oleum. On the other hand, the sulfur trioxide component acts as an internal desiccant for the water formed as a by-product of sulfuric acid sulfonation. Although good yields are readily obtained and a product free of sodium chloride (when the counterion is chloride) is formed, a sulfonated aryl ester is obtained that has significant levels of sodium sulfate. Under optimum reaction conditions the finished product contains approximately 40-45% of the desired sulfonated aryl ester, 55-60% sodium sulfate and 1% sodium chloride. Although sodium sulfate is a component of most finished fabrics washing powders, a process which results in high active ester would permit greater flexibility during the formulation of this material.
Consequently, it is an object of the present invention to provide an improved process for the synthesis of quaternary ammonium or phosphonium substituted carbonic acid esters.
A more specific object of the present invention is to provide an improved process for obtaining the aforementioned carbonic acid esters which limits the amount of sodium chloride and/or sodium sulfate present in the final product.
A further object of the present invention is provide a synthesis of carbonic acid esters that results in a high and relatively reproducible product yield.
A still further object of the present invention is to provide an improved process for obtaining the aforementioned carbonic acid esters but without the necessity of a separate neutralization step.
These and further objects of the present invention will become more evident from the detailed description that follows.